Microwave oven having a magnetron extending directly into the oven cavity

ABSTRACT

A microwave oven is disclosed which eliminates the need for a wave guide and mechanical stirrer while achieving an even distribution of microwave energy within the oven cavity. The microwave oven comprises a housing having an oven cavity defined by conductively bound surfaces. One of the surfaces, preferably the bottom surface, is of a horn-like structure having diverging surfaces facing the interior of the cavity. An aperture is located at the center portion of the horn-like structure to receive the radiating portion of a magnetron tube to enable the magnetron to feed microwave energy directly into the oven cavity. The outer portion of the diverging surfaces adjoins a cylindrical surface, the radius of the cylinder being a multiple of the wave length of the radiated microwaves.

United States Patent 1191 Klemp et al.

1111 3,814,890 1 June 4, 1974 MICROWAVE OVEN HAVING A MAGNETRONEXTENDING DIRECTLY INTO THE OVEN CAVITY [75] Inventors: Eldon JohnKlemp, Mayer; Vernon Edward Cassibo, New Hope, both of Minn.

[73] Assignee: Litton Systems, Inc., Beverly Hills,

' Calif,

[22] Filed: May 16, 1973 [2]] Appl. No.: 360,763

[52] US. Cl...... 219/1055, 343/786 Peterson et al. ..2l9/l0. 55

Attorney, Agent, or Firm-Robert M. Vargo [5 7] ABSTRACT A microwave ovenis disclosed which eliminates the need for a wave guide and mechanicalstirrer while achieving an even distribution of microwave energy withinthe oven cavity. The microwave oven comprises a housing having an ovencavity defined by conductively bound surfaces. One of the surfaces,preferably the bottom surface, is of a horn-like structure havingdiverging surfaces facing the interior of the cavity. An aperture islocated at the center portion of the horn-like structure to receive theradiating portion of a magnetron tube to enable the magnetron to feedmicrowave energy directly into the oven cavity. The outer portion of thediverging surfaces adjoins a cylindrical surface, the radius of thecylinder being a multiple of the wave length of the radiated microwaves.

7 Claims, 4 Drawing Figures PATENTEBJUM M914 3.814 890 SHEU 2 0F 2BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates generally to microwave ovens and more particularly tomicrowave ovens in which the source of microwave energy radiatesdirectly into the oven cavities.

2. Description of the Prior Art In present day conventional microwaveovens, the magnetrons, or other microwave generators, are usuallypositioned entirely outside of the oven cavities. In the constructionsof this type, the radiating portions of the tubes communicate with theoven cavities via wave guides. These wave guides are usuallyrectangularly or cylindrically shaped, having one end enveloping theradiating portion of the magnetron, and the other end communicating witha rectangular feed box which, in turn, opens into the oven cavity.

Present day microwave ovens also have mechanical stirrers positionedeither within the feed boxes or within the oven cavities adjacent theopenings of the feed boxes in order to assist in evenly distributing themicrowave energy throughout the oven cavities.

Although present day microwave ovens operate adequately, they have ashortcoming in that the wave guides and mechanical stirrers add to thecost'of manufacture of the ovens and it would be highly desirable toeliminate these constructions.

Assignees predecessor, the Franklin Oven Division of the StudebakerCorporation, attempted to eliminate the wave guide by extending theradiating ends of the magnetron tubes directly into the oven cavities.This structure is shown in U.S. Pat. Nos. 3,281,567 and 3,308,261,presently assigned to the Assignee of the present application.

However, it was found that the ovens of this type had very poor heatingpatterns and, as a result, still required mechanical stirrers to assistin the distribution of microwave energy within the cavities.

The microwave ovens disclosed in US. Pat. Nos. 3, l 27,494 and3,127,495, also presently assigned to the Assignee of the presentapplication, eliminated the need for mechanical stirrers by providing aconcentrator" 32 which functioned to focus the microwave energy directlyinto the foodstuff. The shortcoming with this construction was that themicrowave energy was concentrated on the central portion of the cavitycooking shelf, leaving the outer areas of the shelf with a much lowerconcentration of energy. Moreover, the magnetrons in these ovens werephysically separated from the oven cavities and required wave guides tocommunicate therewith.

SUMMARY OF THE INVENTION The present invention obviates theabove-mentioned shortcomings by providing a microwave oven thateliminates. the need for a wave guide and stirrer, while achieving aneven distribution of energy within the area to feed microwave energydirectly into the cavity. In this manner, the one surface functions toevenly distribute the microwave energy throughout the oven cavity.

The outer portions of the one surface adjoin a cylindrical surface theradius of which is a multiple of the wave length of the radiatedmicrowaves.

The features of the present invention which are believed to be novel areset forth with particularity in the appended Claims. The presentinvention, both as to its organization and manner of operation, togetherwith a .further advantages thereof, may best be understood by referencesto the following description, taken in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENT Referring now to the drawings, FlGsl illustrates a microwaveoven, generally indicated by arrow 10, having a housing formed by aplurality of outer walls 11.

The housing also includes a front face12 forming an opening into an ovencavity 13. An oven door 14 is pivotally mounted on the front face 12 ofthe oven and is adapted to completely enclose the opening of the cavityl3 and extend over the front face 12 of theoven forming the opening.

Although not restricted thereto, the oven door 14 can be of the typedescribed in Assignees copending US. Pat. applicationsSer. Nos. 266,059and 292,529. The outer end of the oven door 14 includes a latch assembly15 having a plurality of hooked latches 16 which are adapted to extendinto a plurality of openings 17 formed on the front face 12 of the ovenin order to be engaged by a plurality of spring-biased catches (notshown). The latch assembly is disclosed in Assignees copending US. Pat.application Ser. No. 290,000. In accordance with a door and latchassembly of this type, a door release lever I8 is located on the controlpanel 19 of the oven which functions to activate the springbiasedcatches to unlock the hooked latches 16 to open the oven door 14.

The cavity 13 is formed by a plurality of conductively-bound surfaces 20which are formed by a plurality of rectangular walls located on thethree sides and on the top side of the cavity 13. The bottom side ofcavity 13 is hidden from view in FIG. 1 and will be more fully describedhereinafter. A ceramic panel 21, which functions as a shelf, is locatedover the bottom side of the cavity 13.

The side walls 20 and the front face 12 are joined at their corners, asillustrated. .The front face 12 includes an annular cavity 22 whichfunctions as a choke and is adapted to receive a quantity of dielectricmaterial 23. This choke structure is more fully described in Assigneescopending US. Pat. application, Ser. No. 266,059.

In accordance with the present inventiomthe bottom forming the largecircular aperture 26 which is adapted to receive a horn-like structure25.

Referring now to FlGS.,2, 3, and 4, the horn-like structure 25 comprisesa frusto-conical surface 27 diverging outwardly into the interior of theoven cavity 13. As shown in FIG. 2, the conical surface 27 forms aninterior angle a with the adjoining side walls which is greater than 90.As shown in FIG. 3, the diverging surfaces 27 have opposed angles (oneof which is shown as angle B) of less than 180.

The outer portions of the conical surface 27 adjoin a cylindricalsurface 28. In the present embodiment, the radiusof the cylinder isapproximately 4% inches, which is substantially equal to the wavelengthof the microwave energy having a frequency of 2,450 megahertz. The topsurface of the horn-like structure is bent outwardly in a flat plane 29which is adapted to extend over and be supported by the flanged surface24. The central portion 31 of the horn-like structure 25, which formsthe truncated portion thereof, includes an aperture 32 extendingtherethrough. This truncated portion supports a flange 33 which in turnfunctions as a support for a magnetron 34. The magnetron 34 includes aplurality of cooling fins 35 which are adapted to extend around themagnetron tube 36. The magnetron 36 includes a radiating portion 37which is adapted to extend through the aperture 32. As shown in FIG. 4,the conical surface 27 also includes a plurality of air or cooling holes38 mounted on both sides of the aperture 32.

OPERATION As described in the Description Of The Prior Art, a magnetronradiating directly into the microwave oven cavity has already been triedbefore. However, the microwave distribution of these prior ovens was notsatisfactory for commercial utilization. Applicants have found that, byutilizing the horn-like structure 25 in combination with the magnetronextending through the aperture 32 thereof, an even wave distribution isset up within the oven cavity 13 which heretofore was not possible withprior direct feed" microwave ovens. Moreover, Applicants have found thatthe wave distribution canv also be further improved by having theconical surface 27 adjoin a cylindrical surface 28 at its outer edge,and having the radius of the conical surface approximatethe wavelengthof the radiated microwave energy. Because of this discovery, Applicantshave been successful in providing a microwave oven that eliminates theneed for waveguides and mode stirrers while still achieving an evendistribution of microwave energy within the oven cavity.

It should be noted that various modifications can be made to theapparatus while still remaining with the purview of the followingclaims.

What is claimed is: l. A microwave oven comprising: an oven cavitydefined by conductively bounded surfaces;

one of said surfaces extending toward adjoining surfaces at internalangles which are greater than samsfiei'arrae forming a 'turncated conehaving an aperture formed at the truncated end of said cone; and

a source of microwave energy mounted adjacent said one surface, saidsource of microwave energy comprising a magnetron having a radiatingportion extending through said aperture into said cavity.

2. The invention of claim 1 wherein the outer periphery of said onesurface adjoins a cylindrical surface.

3. The invention of claim 2 wherein the radius of said cylindricalsurface is a multiple of the wavelength of the emanating microwaveenergy.

4. The invention of claim 1 wherein said conical surface adjoins acylindrical surface.

5. The invention of claim 4 wherein the radius of said cylindricalsurface is a multiple of the wavelength of the emanating microwaveenergy.

6. A microwave oven comprising:

an oven cavity defined by conductively bounded surfaces;

one of said surfaces forming a horn-like structure having divergingsurfaces facing the interior of said cavity, said diverging surfaceshaving opposed angles of less than the central portion of said horn-likestructure further including an aperture formed therein; and

a source of microwave energy mounted within said horn-like structure,said source of microwave energy comprising a magnetron having aradiating portion extending through said aperture into said cavity.

7. A microwave oven comprising:

an oven cavity defined by conductively bounded surfaces;

one of said surfaces extending toward adjoining surfaces at internalangles which are greater than 90, said one surface further including anaperture formed therein; and

a source of microwave energy mounted adjacent said one surface, saidsource of microwave energy comprising a magnetron having a radiatingportion extending through said aperture into said cavity.

1. A microwave oven comprising: an oven cavity defined by conductivelybounded surfaces; one of said surfaces extending toward adjoiningsurfaces at internal angles which are greater than 90*, said one surfaceforming a turncated cone having an aperture formed at the truncated endof said cone; and a source of microwave energy mounted adjacent said onesurface, said source of microwave energy comprising a magnetron having aradiating portion extending through said aperture into said cavity. 2.The invention of claim 1 wherein the outer periphery of said one surfaceadjoins a cylindrical surface.
 3. The invention of claim 2 wherein theradius of said cylindrical surface is a multiple of the wavelength ofthe emanating microwave energy.
 4. The invention of claim 1 wherein saidconical surface adjoins a cylindrical surface.
 5. The invention of claim4 wherein the radius of said cylindrical surface is a multiple of thewavelength of the emanating microwave energy.
 6. A microwave ovencomprising: an oven cavity defined by conductively bounded surfaces; oneof said surfaces forming a horn-like structure having diverging surfacesfacing the interior of said cavity, said diverging surfaces havingopposed angles of less than 180*, tHe central portion of said horn-likestructure further including an aperture formed therein; and a source ofmicrowave energy mounted within said horn-like structure, said source ofmicrowave energy comprising a magnetron having a radiating portionextending through said aperture into said cavity.
 7. A microwave ovencomprising: an oven cavity defined by conductively bounded surfaces; oneof said surfaces extending toward adjoining surfaces at internal angleswhich are greater than 90*, said one surface further including anaperture formed therein; and a source of microwave energy mountedadjacent said one surface, said source of microwave energy comprising amagnetron having a radiating portion extending through said apertureinto said cavity.